and \(Q(a,z)=\Gamma (a,z)/\Gamma (a)\)  is the normalised incomplete gamma function \((\) see [1]}). The coefficients \(d_n=d_n(\xi ,b)\)  are defined by the generating function
\(\left(\frac{1-\mathrm {e}^{-t}}{t}\right)^{b-1}=\sum _{n=0}^{\infty }d_{n}(t-\xi )^{n}.\) 
